This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Lanthanum carbonate is an oral phosphate binder widely used in cases of kidney failure as precipitated lanthanum phosphate remains in the gut and significant lanthanum is not thought to not cross the gut wall. Very recently, one of us has observed La deposits in human lymph tissue present in macrophages. The chemical nature of these deposits is unclear, however, their presence has clear implications for the safety of LaCO3 therapy. We seek to use EXAFS (together with micro-imaging) to structurally characterize these deposits in fixed tissue samples. Understanding the chemical nature of these deposits has clear importance in re-evaluating the health risks associated with lanthanum therapy.